1. Field of the Invention
The invention relates to a machine-implemented method for forming a release surface of a mold.
2. Description of the Related Art
Referring to FIGS. 1 to 3, a conventional mold 1 for forming a plastic lens 3 is shown to have a mold cavity 101 for receiving a mold core 4, and an inner peripheral surface 102 that defines the mold cavity 101. The inner peripheral surface 102 has a top peripheral portion 1021. An electrical discharge machining process for forming a release surface 1023 of the mold 1 is conducted on the top peripheral portion 1021 using an electrode 5. The release surface 1023 thus formed has a configuration corresponding to that of the electrode 5. In order to improve the smoothness of the release surface 1023, it is required to further polish the release surface 1023 by using oilstones or diamond pastes so as to enhance the releasability of the lens 3 formed thereby from the mold 1.
The conventional electrical discharge machining process has the following disadvantages:
1. Since the electrical discharge machining process is time-consuming and costly, the conventional method of forming the release surface 1023 of the mold 1 involves relatively high production costs. The conventional method is also difficult to control. In addition, the production precision associated with the electrical discharge machining process is limited by a plurality of factors, such as discharge gap, current amount, etc.
2. Referring to FIG. 2, the release surface 1023 of the mold 1 made by the electrical discharge machining process is formed with a plurality of undesired recesses 1024 due to arc discharge. Therefore, the surface roughness of the release surface 1023 is merely about 0.4 μm. An additional manual grinding process is required to polish the release surface 1023 in the conventional method.
3. Although the surface roughness of the release surface 1023 can be improved by the manual grinding process, the recesses 1024 formed on the release surface 1023 of the mold 1 can not be polished away completely by the manual grinding process. Therefore, the peripheral portion of the lens 3 may be abrasive.
4. Referring again to FIG. 2, the release surface 1023 is usually formed with an undesired beveled portion 1025 during the electrical discharge machining process. The beveled portion 1025 of the release surface 1023 should be removed by a further processing, such as by grinding.